Drive transmitting mechanism and image forming apparatus

Abstract

A drive transmitting mechanism configured to rotate the photosensitive drum of a color copier has a driving shaft, a driven shaft, and first and second coupling members. The first coupling member has a projection extending in a diametrical direction. The first coupling member is attached to the driving shaft, with amount of freedom to oscillate in a direction intersecting at right angles to the lengthwise direction of the projection. The second coupling member has a recess in which the projection is fitted. The second coupling member is attached to the driven shaft, with amount of freedom to oscillate in the lengthwise direction of the recess. The first and second coupling members oscillate in the diametrical direction and slide on the contacting surface in a diametrical direction intersecting at right angles to the diametrical direction, thus suppressing the rotational speed change of the driven shaft, which results from the de-centering and declination between the driving shaft and the driven shaft.

1. A drive transmitting mechanism comprising:
 a driving shaft; 
 a driven shaft which is rotated as the driving shaft rotates; and 
 a pair of coupling members which are attached to the driving shaft and the driven shaft, respectively, to transmit a rotational drive force from the driving shaft to the driven shaft, which causes a oscillation in one diametrical direction and a sliding at a contacting surface in another diametrical direction intersecting at right angles to the one diametrical direction, and one of which has two H-shaped projections. 
 
   
   
     2. The drive transmitting mechanism according to  claim 1 , wherein the pair of coupling members are a first coupling member attached to the driving shaft and a second coupling member attached to the driven shaft; the first coupling member has a projection having a predetermined width and extending in the one diametrical direction and a first insertion hole in which the driving shaft is inserted, and is attached to the driving shaft with amount of freedom to oscillate in a diametrical direction that intersects at right angles to a lengthwise direction of the projection; and the second coupling member has a recess in which the projection is fitted, and a second insertion hole in which the driven shaft is inserted, and is attached to the driven shaft with amount of freedom to oscillate in a diametrical direction that intersects at right angles to a lengthwise direction of the recess. 
   
   
     3. The drive transmitting mechanism according to  claim 2 , wherein a predetermined gap is provided between an outer circumference of the driving shaft and a wall of the first insertion hole and extends in the diametrical direction intersecting at right angles with the lengthwise direction of the projection; and a predetermined gap is provided between an outer circumference of the driven shaft and a wall of the second insertion hole and extends in the diametrical direction intersecting at right angles with the lengthwise direction of the recess. 
   
   
     4. The drive transmitting mechanism according to  claim 2 , wherein the first coupling member is attached to the driving shaft, with no amount of freedom to oscillate in the longwise direction of the projection; and the second coupling member is attached to the driven shaft, with no amount of freedom to oscillate in the longwise direction of the recess. 
   
   
     5. The drive transmitting mechanism according to  claim 2 , wherein the driving shaft comprises a first parallel pin provided at a end and extending perpendicular to an axial direction, a compression spring biasing the first coupling member toward the distal end, and a first holding part holding the first compressing spring; and the first coupling member has a first pint receptacle for receiving the first parallel pin and positioning the same parallel to the lengthwise direction of the projection. 
   
   
     6. The drive transmitting mechanism according to  claim 2 , wherein the driven shaft comprises a second parallel pin provided at a end and extending perpendicular to an axial direction and a second holding part holding the second coupling member; and the second coupling member has a second pint receptacle for receiving the second parallel pin and positioning the same parallel to the lengthwise direction of the recess. 
   
   
     7. An image forming apparatus comprising:
 a drive transmitting mechanism having a driving shaft, a driven shaft which is rotated as the driving shaft rotates, and a pair of coupling members which are attached to the driving shaft and the driven shaft, respectively, to transmit a rotational drive force from the driving shaft to the driven shaft, and which causes a oscillation in one diametrical direction and a sliding at a contacting surface in another diametrical direction intersecting at right angles to the one diametrical direction, and one of which has two H-shaped projections; 
 a photosensitive drum unit which rotates around the driven shaft; and 
 a motor unit which rotates the driving shaft. 
 
   
   
     8. The image forming apparatus according to  claim 7 , wherein the pair of coupling members are a first coupling member attached to the driving shaft and a second coupling member attached to the driven shaft; the first coupling member has a projection having a predetermined width and extending in the one diametrical direction and a first insertion hole in which the driving shaft is inserted, and is attached to the driving shaft, with amount of freedom to oscillate in a diametrical direction that intersects at right angles to a lengthwise direction of the projection; and the second coupling member has a recess in which the projection is fitted, and a second insertion hole in which the driven shaft is inserted, and is attached to the driven shaft, with amount of freedom to oscillate in a diametrical direction that intersects at right angles to a lengthwise direction of the recess. 
   
   
     9. The image forming apparatus according to  claim 8 , wherein a predetermined gap is provided between an outer circumference of the driving shaft and a wall of the first insertion hole and extends in the diametrical direction intersecting at right angles with the lengthwise direction of the projection; and a predetermined gap is provided between an outer circumference of the driven shaft and a wall of the second insertion hole and extends in the diametrical direction intersecting at right angles with the lengthwise direction of the recess. 
   
   
     10. The image forming apparatus according to  claim 8 , wherein the first coupling member is attached to the driving shaft, with no amount of freedom to oscillate in the longwise direction of the projection; and the second coupling member is attached to the driven shaft, with no amount of freedom to oscillate in the longwise direction of the recess. 
   
   
     11. The image forming apparatus according to  claim 8 , wherein the driving shaft comprises a first parallel pin provided at a end and extending perpendicular to an axial direction, a compression spring biasing the first coupling member toward the distal end, and a first holding part holding the first compressing spring; and the first coupling member has a first pint receptacle for receiving the first parallel pin and positioning the same parallel to the lengthwise direction of the projection. 
   
   
     12. The image forming apparatus according to  claim 8 , wherein the driven shaft comprises a second parallel pin provided at a end and extending perpendicular to an axial direction and a second holding part holding the second coupling member; and the second coupling member has a second pint receptacle for receiving the second parallel pin and positioning the same parallel to the lengthwise direction of the recess. 
   
   
     13. The image forming apparatus according to  claim 8 , wherein the photosensitive drum unit comprises four photosensitive drums for forming a yellow toner image, a magenta toner image, a cyan toner image and a black toner image, respectively, four coupling members identical to the second coupling member are attached to rotating shafts of the photosensitive drums, respectively, and the motor unit comprises four motors provided for the four coupling members, respectively.